Optimized Preamble and Method for Interference Robust Packet Detection for Telemetry Applications

ABSTRACT

Embodiments provide a receiver having a receiving unit and a synchronization unit. The receiving unit is configured to receive a data packet having a pilot sequence. The synchronization unit is configured to separately correlate the pilot sequence with at least two partial reference sequences corresponding to a reference sequence for the pilot sequence of the data packet, in order to obtain a partial correlation result for each of the at least two partial reference sequences, wherein the synchronization unit is configured to non-coherently add the partial correlation results in order to obtain a coarse correlation result for the data packet.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of copending U.S. application Ser. No.16/140,846, filed on Sep. 25, 2018, which is a continuation of copendingInternational Application No. PCT/EP2016/057014, filed Mar. 31, 2016,which is incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

Embodiments relate to a receiver. Further embodiments relate to a methodfor receiving a data packet. Some embodiments relate to an optimizedpreamble. Some embodiments relate to interference robust detection. Someembodiments relate to preamble splitting. Some embodiments relate to anon-coherent correlation. Some embodiments relate to pilot signaling.

Systems for transmitting small amounts of data, for example, sensordata, from a large number of nodes, such as heating, electricity orwater meters, to a base station are known. A base station receives (andpossibly controls) a large number of nodes. At the base station morecomputing power and a more complex hardware, i.e. a receiver with higherperformance, is available. In the nodes only cheap crystals areavailable, which generally have a frequency offset of 10 ppm or more.

In [G. Kilian, H. Petkov, R. Psiuk, H. Lieske, F. Beer, J. Robert, andA. Neuberger, “Improved coverage for low-power telemetry systems usingtelegram splitting,” in Proceedings of 2013 European Conference on SmartObjects, Systems and Technologies (SmartSysTech), 2013] an improvedcoverage for low-power telemetry systems using telegram splitting isshown.

In [G. Kilian, M. Breiling, H. H. Petkov, H. Lieske, F. Beer, J. Robert,and A. Neuberger, “Increasing Transmission Reliability for TelemetrySystems Using Telegram Splitting,” IEEE Transactions on Communications,vol. 63, no. 3, pp. 949-961, March 2015] an increasing transmissionreliability for telemetry systems using telegram splitting is shown.

In [R. De Gaudenzi, F. Giannetti, and M. Luise, “Signal recognition andsignature code acquisition in CDMA mobile packet communications,” IEEETransactions on Vehicular Technology, vol. 47, no. 1, pp. 196-208,February 1998] a signal recognition and signature code acquisition inCDMA (CDMA=code division multiple access) mobile packet communicationsis discussed.

In [J. Block and E. W. Huang, “Packet Acquisition Performance ofFrequency-Hop Spread-Spectrum Systems in Partial-Band Interference,” inIEEE Military Communications Conference, 2007. MILCOM 2007, 2007, pp.1-7] a packet acquisition performance of frequency-hop spread-spectrumsystems in partial-band interference is discussed.

WO 2013/030303 A2 shows a battery-operated fixed sensor assembly havingunidirectional data transmission.

SUMMARY

According to an embodiment, a receiver may have: a receiving unitconfigured to receive a data packet having a pilot sequence; asynchronization unit configured to separately correlate the pilotsequence with at least two partial reference sequences, in order toobtain a partial correlation result for each of the at least two partialreference sequences; wherein the synchronization unit is configured tonon-coherently add the partial correlation results in order to obtain acoarse correlation result for the data packet; wherein the receivingunit is configured to receive at least two data packets, wherein each ofthe at least two data packets has a pilot sequence; wherein thesynchronization unit is configured to separately correlate the pilotsequence of each of the at least two data packets with at least twopartial reference sequences corresponding to a reference sequence forthe pilot sequence of the corresponding data packet, in order to obtaina partial correlation result for each of the at least two partialreference sequences for each of the at least two data packets; whereinthe synchronization unit is configured to non-coherently add at least apart of the partial correlation results for each of the at least twodata packets in order to obtain a coarse correlation result for each ofthe at least two data packets; wherein the synchronization unit isconfigured to combine at least a part of the coarse correlation resultsof the at least two data packets, in order to obtain a combined coarsecorrelation result.

According to another embodiment, a receiver may have: a receiving unitconfigured to receive data packets, at least two of the data packetshaving a partial pilot sequence of at least two partial pilot sequences;a synchronization unit configured to separately correlate the partialpilot sequences with at least two partial reference sequences, in orderto obtain a partial correlation result for each of the at least twopartial reference sequences; wherein the synchronization unit isconfigured to non-coherently add the partial correlation results inorder to obtain a coarse correlation result for the data packets;wherein the receiving unit is configured to receive further datapackets, at least two of the further data packets having a partial pilotsequence of at least two partial pilot sequences; wherein thesynchronization unit is configured to separately correlate the partialpilot sequences of the further data packets with at least two partialreference sequences, in order to obtain a partial correlation result foreach of the at least two partial reference sequences, wherein thesynchronization unit is configured to non-coherently add the partialcorrelation results for the further data packets in order to obtain acoarse correlation result for the further data packets; wherein thesynchronization unit is configured to combine at least a part of thecoarse correlation results of the data packets and the further datapackets, in order to obtain a combined coarse correlation result.

According to still another embodiment, a method may have the steps of:receiving a data packet having a pilot sequence; separately correlatingthe pilot sequence with at least two partial reference sequencescorresponding to a reference sequence for the pilot sequence of the datapacket, in order to obtain partial correlation results for the at leasttwo partial reference sequences; and non-coherently adding the partialcorrelation results in order to obtain a correlation result for the datapacket; wherein receiving has receiving at least two data packets,wherein each of the at least two data packets has a pilot sequence;wherein separately correlating has separately correlating the pilotsequence of each of the at least two data packets with at least twopartial reference sequences corresponding to a reference sequence forthe pilot sequence of the corresponding data packet, in order to obtaina partial correlation result for each of the at least two partialreference sequences for each of the at least two data packets; whereinnon-coherently adding has non-coherently adding at least a part of thepartial correlation results for each of the at least two data packets inorder to obtain a coarse correlation result for each of the at least twodata packets; wherein the method further has combining at least a partof the coarse correlation results of the at least two data packets, inorder to obtain a combined coarse correlation result.

According to another embodiment, a method may have the steps of:receiving data packets, at least two of the data packets having apartial pilot sequence of at least two partial pilot sequences;separately correlating the partial pilot sequences with at least twopartial reference sequences, in order to obtain a partial correlationresult for each of the at least two partial reference sequences; andnon-coherently adding the partial correlation results in order to obtaina coarse correlation result for the data packets; wherein receiving hasreceiving further data packets, at least two of the further data packetshaving a partial pilot sequence of at least two partial pilot sequences;wherein separately correlating has separately correlating the partialpilot sequences of the further data packets with at least two partialreference sequences, in order to obtain a partial correlation result foreach of the at least two partial reference sequences, wherein thesynchronization unit is configured to non-coherently add the partialcorrelation results for the further data packets in order to obtain acoarse correlation result for the further data packets; wherein themethod further has combining at least a part of the coarse correlationresults of the data packets and the further data packets, in order toobtain a combined coarse correlation result.

Another embodiment may have a non-transitory digital storage mediumhaving stored theron a computer program for performing a method having:receiving a data packet having a pilot sequence; separately correlatingthe pilot sequence with at least two partial reference sequencescorresponding to a reference sequence for the pilot sequence of the datapacket, in order to obtain partial correlation results for the at leasttwo partial reference sequences; and non-coherently adding the partialcorrelation results in order to obtain a correlation result for the datapacket; wherein receiving has receiving at least two data packets,wherein each of the at least two data packets has a pilot sequence;wherein separately correlating has separately correlating the pilotsequence of each of the at least two data packets with at least twopartial reference sequences corresponding to a reference sequence forthe pilot sequence of the corresponding data packet, in order to obtaina partial correlation result for each of the at least two partialreference sequences for each of the at least two data packets; whereinnon-coherently adding has non-coherently adding at least a part of thepartial correlation results for each of the at least two data packets inorder to obtain a coarse correlation result for each of the at least twodata packets; wherein the method further has combining at least a partof the coarse correlation results of the at least two data packets, inorder to obtain a combined coarse correlation result, when said computerprogram is run by a computer.

Another embodiment may have a non-transitory digital storage mediumhaving stored theron a computer program for performing a method having:receiving data packets, at least two of the data packets having apartial pilot sequence of at least two partial pilot sequences;separately correlating the partial pilot sequences with at least twopartial reference sequences, in order to obtain a partial correlationresult for each of the at least two partial reference sequences; andnon-coherently adding the partial correlation results in order to obtaina coarse correlation result for the data packets; wherein receiving hasreceiving further data packets, at least two of the further data packetshaving a partial pilot sequence of at least two partial pilot sequences;wherein separately correlating has separately correlating the partialpilot sequences of the further data packets with at least two partialreference sequences, in order to obtain a partial correlation result foreach of the at least two partial reference sequences, wherein thesynchronization unit is configured to non-coherently add the partialcorrelation results for the further data packets in order to obtain acoarse correlation result for the further data packets; wherein themethod further has combining at least a part of the coarse correlationresults of the data packets and the further data packets, in order toobtain a combined coarse correlation result, when said computer programis run by a computer.

According to still another embodiment, a receiver may have: a receivingunit configured to receive a data packet having a pilot sequence; and asynchronization unit configured to correlate the pilot sequence and areference sequence, in order to obtain a correlation result; wherein thesynchronization unit is configured to apply a weight factor to symbolsof the data packet, or to apply a weight factor to symbols of the pilotsequence, or to apply an individual weight factor to each symbol of thepilot sequence.

According to another embodiment, a receiver may have: a receiving unitconfigured to receive a data packet having a pilot sequence; and asynchronization unit configured to correlate the pilot sequence and areference sequence, in order to obtain a correlation result; wherein thesynchronization unit is configured to use a correlation window fordetecting the data packet, wherein the data packet is detected bydetecting the highest peak of all correlation peaks exceeding apredefined threshold within the correlation window; wherein thecorrelation window is divided into a plurality of time slots, each timeslot having an index associated therewith; wherein if a correlationvalue above the predefined threshold is detected, the highest peakinside the correlation window is searched, wherein the data packetdetection is blocked until the index of the highest correlation peakinside the detection window reaches a defined detection index.

Embodiments provide a receiver comprising a receiving unit and asynchronization unit. The receiving unit is configured to receive a datapacket comprising a pilot sequence. The synchronization unit isconfigured to separately correlate the pilot sequence with at least twopartial reference sequences corresponding to a reference sequence forthe pilot sequence of the data packet, in order to obtain a partialcorrelation result for each of the at least two partial referencesequences, wherein the synchronization unit is configured tonon-coherently add the partial correlation results in order to obtain acoarse correlation result for the data packet.

It is the idea of the present invention to synchronize a data packet bycorrelating the data packet (or a pilot sequence of the data packet)with at least two partial reference sequences, each of which is shorterthan the pilot sequence contained within the data packet, in order toobtain, a partial correlation result for each of the at least twopartial reference sequences, wherein the partial correlation results arenon-coherently added thereby reducing some effects of a transmissionchannel over which the data packet is reduced, in order to improvesynchronization performance.

Further embodiments provide a method, comprising:

-   -   receiving a data packet comprising a pilot sequence;    -   separately correlating the pilot sequence with at least two        partial reference sequences corresponding to a reference        sequence for the pilot sequence of the data packet, in order to        obtain partial correlation results for the at least two partial        reference sequences; and    -   non-coherently adding the partial correlation results in order        to obtain a correlation result for the data packet.

Further embodiments provide a receiver comprising a receiving unit and asynchronization unit. The receiving unit is configured to receive datapackets (e.g., at least two data packets), at least two of the datapackets (e.g., each of the at least two data packets) comprising apartial pilot sequence of at least two partial pilot sequences. Thesynchronization unit is configured to separately correlate the partialpilot sequences with at least two partial reference sequences, in orderto obtain a partial correlation result for each of the at least twopartial reference sequences. Thereby, the synchronization unit isconfigured to non-coherently add the partial correlation results inorder to obtain a coarse correlation result for the two data packets.

Further embodiments provide a method, comprising:

-   -   receiving at least two data packets, each of the at least two        data packets comprising a partial pilot sequence of at least two        partial pilot sequences;    -   separately correlating the partial pilot sequences with at least        two partial reference sequences, in order to obtain a partial        correlation result for each of the at least two partial        reference sequences; and    -   non-coherently adding the partial correlation results in order        to obtain a coarse correlation result for the two data packets.

Further embodiments provide a receiver comprising a receiving unit and asynchronization unit. The receiving unit is configured to receive a datapacket comprising a pilot sequence. The synchronization unit isconfigured to correlate the pilot sequence and a reference sequence, inorder to obtain a correlation result. Thereby, the synchronization unitis configured to apply a weight factor to symbols of the data packet, orto apply a weight factor to symbols of the pilot sequence, or to applyan individual weight factor to each symbol of the pilot sequence.

Further embodiments provide a receiver comprising a receiving unit and asynchronization unit. The receiving unit is configured to receive a datapacket comprising a pilot sequence. The synchronization unit isconfigured to correlate the pilot sequence and a reference sequence, inorder to obtain a correlation result. Thereby, the synchronization unitis configured to use a correlation window for detecting the data packet,wherein the data packet is detected by detecting the highest peak of allcorrelation peaks exceeding a predefined threshold within thecorrelation window.

In some embodiments, non-coherently adding the partial correlationresults involves discarding the phase information after the correlation,e.g., by adding absolute values or squared absolute values orapproximated absolute values of the partial correlation results.

In some embodiments, the synchronization unit can be configured tonon-coherently add the partial correlation results by adding absolutevalues or squared absolute values or approximated absolute values of thepartial correlation results.

In some embodiments, the at least two partial reference sequences can beat least two different parts of the reference sequence.

In some embodiments, the data packet can comprise at least two partialreference sequences as the reference sequence.

In some embodiments, the receiving unit can be configured to receive atleast two data packets, wherein only a part of the at least two datapackets comprises a pilot sequence, for example, the receiving unit canbe configured to receive a data packet without a pilot sequence.

In some embodiments, the receiving unit can be configured to receive atleast two data packets, wherein each of the at least two data packetscan comprise a pilot sequence.

The synchronization unit can be configured to separately correlate thepilot sequence of each of the at least two data packets with at leasttwo partial reference sequences corresponding to a reference sequencefor the pilot sequence of the corresponding data packet, in order toobtain a partial correlation result for each of the at least two partialreference sequences for each of the at least two data packets. Further,the synchronization unit can be configured to non-coherently add atleast a part of the partial correlation results for each of the at leasttwo data packets in order to obtain a coarse correlation result for eachof the at least two data packets, and to combine at least a part of thecoarse correlation results of the at least two data packets, in order toobtain a combined coarse correlation result.

The synchronization unit can be configured to combine the coarsecorrelation results of the at least two data packets by using a sum orapproximations of an ideal Neyman-Pearson detector of the coarsecorrelation results of the at least two data packets.

In some embodiments, the at least two data packets can be parts of atelegram which can be transmitted separated into the at least two datapackets. The receiver can further comprise a data packet combining unitconfigured to combine the at least two data packets in order to obtainthe telegram.

The synchronization unit can be further configured to coherently add thepartial correlation results, in order to obtain a fine correlation forthe data packet.

Further, if the combined coarse correlation result exceeds a predefinedthreshold, the synchronization unit can be further configured tocoherently add the partial correlation results for each of the at leasttwo data packets in order to obtain a fine correlation result for eachof the at least two data packets. For example, the synchronization unitcan be configured to combine the fine correlation results of the atleast two data packets, in order to obtain a combined fine correlationresult.

The synchronization unit can be configured to normalize the coarsecorrelation results of the at least two data packets and to combine thenormalized coarse correlation results of the at least two data packets,in order to obtain a coarse correlation result for the telegram.

Further, the synchronization unit can be configured to normalize thefine correlation results of the at least two data packets and to combinethe normalized fine correlation results of the at least two datapackets, in order to obtain a combined fine correlation result.

In some embodiments, the synchronization unit can be configured toestimate a frequency offset of the data packet.

For example, the synchronization unit can be configured to estimate thefrequency offset in case of large offsets (e.g., greater than or equalto the data rate) by oversampling in the frequency domain and parallelcorrelation on several frequencies. The correlation result with thehighest peak delivers the coarse frequency offset.

Further, the synchronization unit can be configured to estimate thefrequency offset in case of small offsets (e.g., smaller than the datarate) based on phase difference between adjacent symbols

Further, the synchronization unit can be configured to estimate thefrequency offset in case of sufficiently large partial pilot sequences(e.g., dependent on a signal-to-noise ratio) directly based on thesepartial pilot sequences.

Further, the synchronization unit can be configured to estimate thefrequency offset based on the coarse correlation result to obtain acoarse frequency offset, or based on the fine correlation result toobtain a fine frequency offset.

The receiver can comprise a header extraction unit configured to extracta header information from the data packet coded in a phase shift of thepilot sequence by applying a frequency correction to the data packetusing the estimated frequency offset and estimating the phase shift ofthe pilot sequence.

In some embodiments, the synchronization unit can be configured tonormalize symbols of the pilot sequence to obtain a normalized pilotsequence and to separately correlate the normalized pilot sequences withthe at least two partial reference sequences.

In some embodiments, the synchronization unit can be configured tocalculate a variance of the partial correlation results for the datapacket and to detect the data packet if the variance of the partialcorrelation results for the data packet is smaller than or equal to apredefined threshold.

In some embodiments, the synchronization unit can be configured to applya weight factor to symbols of the data packet, or to apply an individualweight factor to symbols of each of the at least two partial pilotsequences, or to apply an individual weight factor to each symbol of theat least two partial pilot sequences or to apply an individual weightfactor to each of the at least two partial reference sequences, or toapply an individual weight factor to each symbol of the data packet.

In some embodiments, the synchronization unit can be configured todetect a main lobe and side lobes of the correlation and to provide thedetected main lobe as correlation result using known distances betweenthe main lobe and the side lobes.

In some embodiments, the synchronization unit can be configured to use acorrelation window for detecting the data packet, wherein the datapacket is detected by detecting the highest peak of all correlationpeaks exceeding a predefined threshold within the correlation window.

Embodiments provide a computational efficient frequency insensitivedetection of telegrams by use of partial correlation of preambles withinsub-packets and combining over many sub-packets

Further embodiments provide a robust transmission of (additional) headerinformation using detection and synchronization pilots with no or onlysmall impact on the receiver performance by using phase offsets fortransmission of partial preambles parts (partial preambles) of thepilots of the sub-packets.

Further embodiments provide an interference robust detection.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention will be described herein makingreference to the appended drawings, in which:

FIG. 1 shows a schematic block diagram of a receiver, according to anembodiment;

FIG. 2a shows a schematic view of a data packet (sub-packet), accordingto an embodiment;

FIG. 2b shows a schematic view of a data packet (sub-packet), accordingto a further embodiment;

FIG. 2c shows a schematic view of a data packet (sub-packet), accordingto a further embodiment;

FIG. 2d shows a schematic view of a data packet (sub-packet), accordingto a further embodiment;

FIG. 2e shows a schematic view of a data packet (sub-packet), accordingto a further embodiment;

FIG. 2f shows a schematic view of a data packet (sub-packet), accordingto a further embodiment;

FIG. 3 shows a schematic view of a synchronization of a data packet,according to EP 2 914 039 A1;

FIG. 4 shows a schematic view of a synchronization of a data packet,according to an embodiment;

FIG. 5 shows in a diagram an amplitude of an autocorrelation function ofBarker-7 code plotter over time;

FIG. 6 shows in a diagram an amplitude of an autocorrelation function ofBarker-7 code with a higher side lobe caused by an interferer plotterover time;

FIG. 7a shows a schematic view of a data packet with two partial pilotsequences and a data sequence, as well as a long interferer overlayingthe data packet, for three different time slots;

FIG. 7b shows in diagrams receive power and normalized received powerfor sub-packet or telegram wide normalization plotted over time for eachof the three different time slots;

FIG. 8a shows a schematic view of a data packet with two partial pilotsequences and a data sequence, as well as a short interferer overlayingthe data packet, for three different time slots;

FIG. 8b shows in diagrams receive power and normalized received powerfor sub-packet or telegram wide normalization plotted over time for eachof the three different time slots;

FIG. 9a shows a schematic view of a data packet with two partial pilotsequences and a data sequence, as well as a short interferer overlayingthe data packet, for three different time slots;

FIG. 9b shows in diagrams receive power and normalized received powerfor symbol wide normalization plotted over time for each of the threedifferent time slots;

FIG. 10 shows in a diagram a plurality of data packets which are part ofa telegram which is transmitted separated into the plurality of datapackets over a communication channel together with a schematic view of acalculation of a variance over all (or at least a part of) the datapackets, according to an embodiment;

FIG. 11 shows a schematic view of three data packets, each of the datapackets having two partial pilot sequences, and of a weighting of thepilot sequences performed by applying individual weighting factor toeach of the partial pilot sequences for each data packet, according toan embodiment;

FIG. 12 shows in a diagram an amplitude of a correlation functionplotted over time, according to an embodiment;

FIG. 13 shows a schematic view of a detection window, according to anembodiment;

FIG. 14 shows a flow-chart of a method for detecting a data packet usinga detection window, according to an embodiment;

FIG. 15 shows in three diagrams amplitudes of correlation resultsplotted over time for three different time slots as well as thethreshold and the detection window used for detecting the data packet,according to an embodiment;

FIG. 16 shows in a diagram a plurality of data packets which are part ofa telegram which is transmitted separated into the plurality of datapackets over a communication channel and a schematic view of a partlycorrelation over three of the data packets, according to an embodiment;

FIG. 17 shows a flowchart of a method for receiving a data packet,according to an embodiment;

FIG. 18 shows a schematic block diagram of a receiver, according to anembodiment; and

FIG. 19 shows a flowchart of a method for receiving a data packet,according to an embodiment.

DETAILED DESCRIPTION OF THE INVENTION

Equal or equivalent elements or elements with equal or equivalentfunctionality are denoted in the following description by equal orequivalent reference numerals.

In the following description, a plurality of details are set forth toprovide a more thorough explanation of embodiments of the presentinvention. However, it will be apparent to one skilled in the art thatembodiments of the present invention may be practiced without thesespecific details. In other instances, well-known structures and devicesare shown in block diagram form rather than in detail in order to avoidobscuring embodiments of the present invention. In addition, features ofthe different embodiments described hereinafter may be combined witheach other, unless specifically noted otherwise.

FIG. 1 shows a schematic block diagram of a receiver 100 according to anembodiment. The receiver 100 comprises a receiving unit 102 and asynchronization unit 104. The receiving unit 102 is configured toreceive a data packet 106 comprising a pilot sequence 108.

For example, the receiving unit 102 can be configured to receive anddemodulate a signal transmitted from a transmitter over a communicationchannel to the receiver 100, and to provide based thereon a data streamcomprising the data packet 106.

The data packet 106 can comprise the pilot sequence 108 and one or moredata sequences 110 arranged before, after or between (not shown in FIG.1, see, for example, FIG. 2) the pilot sequence 108. The data packet 106can be part of a telegram which is transmitted separated into aplurality of data packets (or sub-packets).

The synchronization unit 104 is configured to separately correlate thepilot sequence 108 with at least two partial reference sequences 112_1to 112_n (n can be a natural number greater than or equal to two), inorder to obtain a partial correlation result 116_1 to 116_n for each ofthe at least two partial reference sequences 112_1 to 112_n, wherein thesynchronization unit 104 is configured to non-coherently add the partialcorrelation results 116_1 to 116_n in order to obtain a coarsecorrelation result 118 for the data packet 106.

For example, the synchronization unit 104 can be configured toseparately correlate the data stream provided by the receiving unit 102with the at least two partial reference sequences 112_1 to 112_n.

Each of the at least two partial reference sequences 112_1 to 112_n canbe shorter than the pilot sequence 108 of the data packet.

The at least two partial reference sequences 112_1 to 112_n cancorrespond to a reference sequence 114 for the pilot sequence 108 of thedata packet 106, i.e. the at least two partial reference sequences 112_1to 112_n can be parts of a reference sequence 114 for the pilot sequence108 of the data packet. Assuming an ideal communication channel betweentransmitter and receiver 100, the reference sequence 108 and the pilotsequence are the same. Each of the at least two partial referencesequences 112_1 to 112_n can be shorter than the reference sequence 114.For example, the reference sequence 114 can be divided into at least two(or n) parts (or sets), in order to obtain the at least two (or n)partial reference sequences 112_1 to 112_n, i.e. a first part of thereference sequence 114 is a first of the at least two partial referencesequences 112_1 to 112_n and a second part of the reference sequence 114is a second of the at least two partial reference sequences 112_1 to112_n, and so on (if applicable).

The synchronization unit 104 can be configured to non-coherently add thepartial correlation results by adding absolute values or squaredabsolute values or approximated absolute values of the partialcorrelation results.

Pilots (or a sequence of pilot symbols (pilot sequence)) can betransmitted within a data packet or sub-packet. Pilots can be used forat least one out of detection of the packet, time synchronization andfrequency synchronization.

There are different ways for positioning of the pilots within thesub-packet as will become clear from the following discussion of FIGS.2a to 2 f.

FIG. 2a shows a schematic view of a data packet (sub-packet) 106according to an embodiment. The data packet 106 comprises a pilotsequence 108 and two data sequences 110 arranged before and after thepilot sequence 108. Symbols of the data packet 106 are indicated using acomplex vector illustration, i.e. each arrow may illustrate one symbolof a modulation method used for transmitting the data packet.

As shown in FIG. 2a , in embodiments, the pilot sequence 108 cancomprise at least two partial pilot sequences 108_1 to 108_n, i.e. thepilot sequence 108 can be separated into at least two partial pilotsequences 108_1 to 108_n. Thereby, each of the partial pilot sequences108_1 to 108_n may have a corresponding partial reference sequence 112_1to 112_n, for example, a first partial reference sequence 112_1 may havea corresponding first partial pilot sequence 108_1 (i.e. a correlationpeak will be maximized when correlating the first partial referencesequence 112_1 and the first partial pilot sequence 108_1) and a secondpartial reference sequence 112_2 may have a corresponding second partialpilot sequence 108_2 (i.e. a correlation peak will be maximized whencorrelating the second partial reference sequence 112_2 and the secondpartial pilot sequence 108_2), and so on (if applicable).

FIG. 2b shows a schematic view of a data packet (sub-packet) 106according to an embodiment. The data packet 106 comprises two partialpilot sequences 108_1 and 108_2 and a data sequences 110 arrangedbetween the two partial pilot sequences 108_1 and 108_2. Symbols of thedata packet 106 are indicated using a complex vector illustration, i.e.each arrow may illustrate one symbol of a modulation method used fortransmitting the data packet.

FIG. 2c shows a schematic view of a data packet (sub-packet) 106according to an embodiment. The data packet 106 comprises two partialpilot sequences 108_1 and 108_2 and a data sequences 110 arrangedbetween the two partial pilot sequences 108_1 and 108_2. Thereby, thesecond partial pilot sequence 108_2 is longer (e.g., twice as long) thanthe first reference sequence 108_1. Symbols of the data packet 106 areindicated using a complex vector illustration, i.e. each arrow mayillustrate one symbol of a modulation method used for transmitting thedata packet.

FIG. 2d shows a schematic view of a data packet (sub-packet) 106according to an embodiment. The data packet 106 comprises two partialpilot sequences 108_1 and 108_2 and three data sequences 110 arrangedbefore, after and between the two partial pilot sequences 108_1 and108_2. Symbols of the data packet 106 are indicated using a complexvector illustration, i.e. each arrow may illustrate one symbol of amodulation method used for transmitting the data packet.

FIG. 2e shows a schematic view of a data packet (sub-packet) 106according to an embodiment. The data packet 106 comprises two partialpilot sequences 108_1 and 108_2 and three data sequences 110 arrangedbefore, after and between the two partial pilot sequences 108_1 and108_2. Symbols of the data packet 106 are indicated using a complexvector illustration, i.e. each arrow may illustrate one symbol of amodulation method used for transmitting the data packet. Symbols of thedata packet 106 are indicated using a complex vector illustration, i.e.each arrow may illustrate one symbol of a modulation method used fortransmitting the data packet.

FIG. 2f shows a schematic view of a data packet (sub-packet) 106according to an embodiment. The data packet 106 consists of a pilotsequence 108 that is separated (or can be separated by the receiver 100)into the two partial pilot sequences 108_1 and 108_2. Symbols of thedata packet 106 are indicated using a complex vector illustration, i.e.each arrow may illustrate one symbol of a modulation method used fortransmitting the data packet.

Pilots 108 may but are not required to use the same modulation scheme asthe data part 110. The pilots 108 of each data packet 106 can be splitat least into two parts, here as example p1 (108_1) and p2 (108_2). Theat least two parts p1 (108_1) and p2 (108_2) may but are not required tobe temporally separated. The signal over time of p1 (108_1) and p2(108_2) can be known to the receiver 100. The signal received at thereceiver 100 can be affected by channel impairments such as noise. Dueto an offset of the crystals used the transmitter and the receiver 100the exact time, frequency offset and phase offset of the received signalare initially not known to the receiver 100.

In order to detect the signal the receiver 100 might perform a crosscorrelation of the whole signal p1 (108_1) and p2 (108_2) versus thereceived signal. In the presence of a frequency offset this will reducethe correlation peak.

EP 2 914 039 A1 proposes to use sub-packet version in order to reducethese effects, as will become clear from the discussion of FIG. 3.

In detail, FIG. 3 shows a schematic view of the synchronization of thedata packet 106 according to EP 2 914 039 A1. The data packet 106received corresponds to the data packet 106 shown in FIG. 2b . However,the data packet 106 is affected by a frequency offset, which isindicated in FIG. 3 by a rotation of the vectors used for describing thesymbols of the data packet.

Further, in FIG. 3, the reference sequences (or correlation sequences)112_1 and 112_2, the correlation products 115_1 and 115_2 obtained bycorrelating the reference sequences (or correlation sequences) 112_1 and112_2 with the data packet 106, and the correlation result 118 as sumover all products are shown. Thereby, a length of the correlation peakis reduced due to the frequency offset.

For larger frequency offsets even the correlation peak of the sub-packetshown in FIG. 2a might be reduced in a significant manner.

Detection Combined Partial Preamble Correlation

In contrast to FIG. 3, embodiments provide detection combined partialpreamble correlation (cppc). Thereby, a non-coherent combination of atleast two received partial preamble parts (rp1, rp2, . . . ) withinsmall sub-packets may be used.

For example, some embodiments propose a non-coherent combination of codematched filter outputs for CDMA detection. In a long stream of datamultiple matched filter outputs of single CDMA symbols can be combined.

Further, embodiments propose different ways of non-coherent combinationof correlation results of the single hops of a frequency hop spreadspectrum system. Correlation results of single hops can be combined.

As will become clear from the following discussion, first, anon-coherent combination on sub-packet (or HOP) level can be used (seeFIG. 4), and second, a combination of the already combined sub-packetlevel results to an overall result can be used.

FIG. 4 shows a schematic view of the synchronization of the data packet106 according to an embodiment. The data packet 106 received correspondsto the data packet 106 shown in FIG. 2b . However, the data packet 106is affected by a frequency offset, which is indicated in FIG. 4 by arotation of the vectors used for describing the symbols of the datapacket.

Further, in FIG. 4, the at least two partial reference sequences (orcorrelation sequences) rp1 (108_1) and rp2 (108_2), the correlationproducts cp1 (115_1) and cp2 (115_2) obtained by correlating the atleast two partial reference sequences (or correlation sequences) 108_1and 108_2 with the data packet 106, the partial correlation results c1(116_1) and c2 (116_2) obtained by summing the individual correlationproducts cp1 (115_1) and cp2 (115_2) (e.g., using the equationscp1=rp1*conj(p1) and cp2=rp2*conj(p2)), and the coarse correlationresult spm (118) for the data packet 106 obtained by non-coherentlyadding the partial correlation results c1 (116_1) and c2 (116_2) areshown.

In other words, as indicated in FIG. 4, a correlation of the firstpartial pilot sequence rp1 (108_1) and the second partial pilot sequencerp2 (108_2) with the first partial reference sequence p1 (112_1) and thesecond partial reference sequence p2 (112_2) is performed, respectively.This results in the partial correlation results c1 (116_1) and c2(116_2).

Further, a non-linear operation like abs( ), an approximation of abs( ),or any other non-linear operation can be applied to the partialcorrelation results c1 (116_1) and c2 (116_2) of the partial preambleparts of the sub-packets or any approximation of the idealNeyman-Pearson detector. This results in values I1 and I2. Addition ofthe values results in the sub-packet preamble metric spm=I1+I2. In thepresence of frequency offset the spm=I1+I2 is longer as for directcorrelation cdirect=abs(c1+c2), even for the sub-packet shown in FIG. 2a.

This provides the following advantage. The method is robust versusfrequency offset. In the presence of large crystal offsets betweentransmitters and receivers less sub-band have to be searched in order tofind a preamble.

As already mentioned, the data packet 106 can be part of a telegramwhich is transmitted separated into a plurality of data packets (orsub-packets).

The receiving unit 102 can be configured to receive at least two datapackets 106, wherein each of the at least two data packets 106 comprisesa pilot sequence 108, wherein the at least two data packets 106 areparts of a telegram which is transmitted separated into the at least twodata packets 106. The synchronization unit 104 can be configured toseparately correlate the pilot sequence 108 of each of the at least twodata packets with at least two partial reference sequences p1 (112_1)and p2 (112_2) corresponding to a reference sequence for the pilotsequence of the corresponding data packet 106, in order to obtain apartial correlation result c1 (116_1) and c2 (116_2) for each of the atleast two partial reference sequences p1 (112_1) and p2 (112_2) for eachof the at least two data packets 106. Further, the synchronization unit104 can be configured to non-coherently add the partial correlationresults c1 (116_1) and c2 (116_2) for each of the at least two datapackets 106 in order to obtain a coarse correlation result spm (118) foreach of the at least two data packets 106. Further, the synchronizationunit 104 can be configured to combine the coarse correlation results spm(118) of the at least two data packets 106, in order to obtain a coarsecorrelation result for the telegram.

In other words, the coarse correlation results spm (118) of thesub-packets (which also can be based on one partial correlation only)can be combined to a telegram preamble metric (or coarse correlationresult for the telegram) tpm. Combining can be, for example, performedby a simple sum or by other approximations of ideal Neyman-Pearsondetector.

This has the advantage that less computational power is needed.

For example, 30 sub-packets with two partial preambles in eachsub-packet can be used, e.g., 15 times the sub-packet version a) shownin FIG. 2a and 15 times the sub-packet version b) shown in FIG. 2b .Using only one sum in each time step 60 additions are used, i.e. 30sub-packets multiplied by 2 partial preambles. If, as proposed, twosuccessive sums are used, computational power can be reduced. In eachtime step spm over sub-packet version a) and one sum over sub-packetversion b) can be calculated. The resulting spm a) and spm b) can bestored in a memory. Then a sum over the pre-calculated spm a) and spm b)can be calculated over the according values stored in memory. In thatcase, only two additions for the pre-calculation and 30 additions forthe final sum are used.

The synchronization unit 104 can be further configured, if the coarsecorrelation result for the telegram exceeds a predefined threshold, tocoherently add the partial correlation results c1 (116_1) and c2 (116_2)for each of the at least two data packets 106 in order to obtain a finecorrelation result for each of the at least two data packets 106.Further, the synchronization unit 104 can be configured to combine thefine correlation results of the at least two data packets, in order toobtain a fine correlation result for the telegram.

In other words, a first search (or stage) with non-coherent addition canbe combined with a second search (or stage) with coherent addition.

The earlier described technique with non-coherent addition of at leasttwo sync parts of one sub packet can be used. Afterwards the sum overall sub packets can be calculated. This value can be compared to athreshold and if the value is above the threshold a second correlationcan be done.

The second stage can calculate the correlation with coherent addition ofall parts inside a sub packet or over all hops of a telegram. This isdone as a hypothesis test for many different hypothetical frequencyoffsets. The value resulting on coherent addition of the sub-correlationresults is also compared against a threshold. If the value is in thedetection range, the begin of a packet is detected. The first stage(non-coherent addition) yields a coarse frequency offset, which isneeded for the second stage. The second stage provides a more precisefrequency offset, which can be used in the following decoder.

This technique uses a two-stage detection. The second correlation ismuch more frequency sensitive than the first one, so there are morecalculations on different frequency offsets. To reduce the computationpower the second correlation is only done, if the first stage detects apacket. Therefore the increase of computation power is very low.

This technique also provides a fine estimated frequency offset, which ishelpful for the decoder. The decoder saves computation power because itdoesn't have to calculate the frequency offset again.

Using Pilots for Signalling of Header Information

In the following embodiments are described which used the pilots forsignalling of header information.

The data packet 106 can comprise header information coded in a phaseshift of the pilot sequence 108. The receiver 100 can comprise a headerextraction unit configured to extract the header information from thedata packet by applying a frequency correction to the data packet usingan estimated frequency offset of the data packet 106 and estimating thephase shift of the pilot sequence.

If combined partial preamble correlation (cppc) or other schemes areused, the performance of the preamble detector can be totallyinsensitive or insensitive in a tolerable manner against phase rotationsof the transmitted partial pilot sequences p1 (108_1) and p2 (108_2).

The transmitter can add an arbitrary phase shift phi in the range of[−pi, pi] to the partial pilot sequences p1 (108_1) and p2 (108_2).

Proposed shifting schemes are among others

-   -   p1′=p1*exp(2*pi*phi), p2′=p2*exp(−2*pi*phi), i.e. p1 and p2 are        shifted in opposite direction;    -   p1′=p1, p2′=p2*exp(−2*pi*phi), i.e. only p2 is shifted;    -   p1′=p1*exp(2*pi*phi), p2′=p2, i.e. only p1 is shifted;    -   wherein p1′ is the phase shifted version of p1 and p2′ is the        phase shifted version of p2.

Furthermore, a combination of the described schemes is possible. Alldifferential phase modulation schemes might be used. Phase shifts can becalculated for all or a subset of the partial pilotsequences/sub-packets by encoding the header bits to be transmitted bwith a forward error correction (FEC) code resulting in transmitter codesymbols c. Golay Codes, BCH Codes, Convolutional codes or Turbo Codes orLDPC Codes or other codes might be used. The code symbols can be mappedto phase shifts phi_i with index i for the partial pilotsequences/sub-packet i.

Generating p1 to p2 Phase Offset if the Preamble is MSK/GMSK Modulated

Subsequently, a generation of phase offsets of the partial pilotsequences p1 (108_1) and p2 (108_2) of a MSK (MSK=minimum shift keying)or GMSK (GMSK=Gaussian filtered minimum shift keying) modulated preamble108 is described.

If the system uses MSK or GMSK modulation for the packets, thetransmitters can easily adopted to introduce a phase offset for thepartial pilot sequences p1 (108_1) or p2 (108_2). Further on we willconcentrate on p2.

If differential MSK/GMSK is used, then the first bit of p2 can beinverted and/or the first symbol of the data part after p2 can beinverting, if existing.

If precoded MSK/GMSK is used, then all symbols of p2 can be inverted.

Decoding the Received Phase Shifts

The receiver 100 (or the synchronization unit 104) can be configured to:

-   -   1. perform a rough estimate of the frequency offset f_r of the        received signal by inspection of the partial preambles (e.g.,        the phase difference of the received symbols in cp1 and cp2 can        be analysed);    -   2. perform a rough frequency correction rp1′=rp1*exp(−2*p*f_r)        and rp2′=rp2*exp(−2*p*f_r)    -   3. estimate the phase offset phi′ between rp1′ and rp2′ (e.g. by        calculation of phi′=arg(c1*conj(c2)), note that the design of p1        and p2 can be preformed such that the rough frequency correction        is sufficient that phi′ can be estimated without phase ambiguity        in most cases);    -   4. to calculate a log-likelihood Ilr_i or a simplified        estimation of the transmitted phi_i; and    -   5. decode the transmitted header bit vector h_e out of the Ilr_i        by the channel decoder.

Removement of Transmitted Phase Offsets in the Preamble

When the vector h_e has been decoded at the receiver it can be encodedagain. This gives the list of phase offsets phi_e_i.

This phase offsets phi_e_i can be used to remove the phase shift of thereceived partial preambles (rp2 here) in the received signal. Thus, thedecoder can continue decoding the received sub-packets in the same wayas without transmission of header information.

Interference Robust Detection

The transmission is usually done in unlicensed bands (e. g. ISM(ISM=industrial, scientific and medical) bands) and/or the sensor nodesare not synchronized with the base station. Therefore interference withother systems using the same time slot will occur. If the system is notsynchronized with the base station, interference with other sensor nodeswill also occur.

This interference negatively influences the performance of the detectionin the receiver. On the one hand it can reduce the correlation result ofthe correlation of the main lobe and on the other hand it will increaseside lobes, which are unwanted. These side lobes are shown in FIG. 5 fora barker code with length of 7. The side lobes are peaks, which are notin the middle of the autocorrelation function and are unequal to zero.

To avoid false detection at side lobes the threshold needs to be greaterthan the highest side lobe.

In the autocorrelation function 13 values are calculated, so one timeslot equals one symbol time. It's also possible to use more time slots(e. g. one time slot equals ½ symbol time) or less time slots (e. g. onetime slot equals 2 symbol times).

If an interferer with strong power at the receiver is on air, thecorrelation result is in most cases at this time slot very high and afalse detection can occur. This is shown in FIG. 6. An interferer hasincreased the correlation result and created an “interference peak” sothe value is above the defined threshold, which leads to falsedetection.

There are some techniques to decrease the number of false detections, incase of interference and/or for non-ideal correlation sequences, whichare described in the following. They can be used standalone or they canused in combination to achieve a better result.

Normalization

If an interferer occurs in the used band of the wanted signal,distortion of the transmitted symbols is possible. Distortion in thiscase is an arbitrary phase- and amplitude-offset on each symbol duringthe transmit time of an interferer.

To reduce the impact of such interferers, normalization is done. Thisnonlinear operation equals the power over one sub packet, telegram or ofeach transmitted symbol.

In other words, for sub packet wise normalization e. g. the mean powerover the length of one sub packet is calculated. This calculation isdone for each time slot separately. Pmean[m]=sum(Pin)/N (Pin are thepower of the symbols inside the sub packet length, N the length of onesub packet in symbols, m is the index for each time slot).

This value is applied to all symbols of the length of one sub packetinside the according time slot. For example, the receive power of eachsymbol is divided by the mean power of one sub packet(Pout[k]=Pin[k]/Pmean[m], k=symbol number inside the sub packet length).

FIG. 7a shows a schematic view of a data packet 106 with two partialpilot sequences 108_1 and 108_2 and a data sequence 110, wherein thedata packet 106 is overlaid (or superimposed) by a long interferer 130.FIG. 7b shows in diagrams receive power and normalized received powerplotted over time for each of the three time slots of FIG. 7 a.

In detail, FIGS. 7a and 7b show an example for this technique, withthree different time slots. For each time slot the length of one subpacket in symbols is cut. The second time slot shows the perfect one,where all symbols of the sub packet are inside the cut area. The firstand the last one are too early or too late.

On all three time slots an interferer is the whole time active and it isassumed that the power of the interferer is much higher than the symbolpower. The receive power (sum of signal plus interferer in the usedband) is shown as line 132 in all three cases in the diagrams of FIG. 7b.

After the cut, the mean power with the equation described above iscalculated for each time slot. In each time slot each symbol is dividedby this mean power value, described with the above equation. Thereforethe mean power in each time slot is now equal to one. If no interfereris during a transmission on air, the mean power after normalization isalso equal to one. The impact of a completely interfered sub packet isnow the same, as one without interferer in it. The normalized receivepower is shown as line 134 in all three cases in the diagrams of FIG. 7b.

It is also possible for the calculation of the normalization value, tocut more than the length of one sub packet, e. g. the length of two subpackets. In this case we also cut ½ of the length before and behind thesub packet. The longer the used length for the calculation of thenormalization value is, the better is the result against shortinterferer.

A short interferer increases only a subset of symbols inside the area,which is used for the calculation. If only a small subset of symbol isinterfered, the impact of these symbols is very low.

This method works fine if the duration of an interferer is much largerthan the duration of one sub packet. If the duration is in the sameregion or shorter than the sub packet duration, this normalizationyields unusable results. This problem is explained with an example inFIGS. 8a and 8 b.

FIG. 8a shows a schematic view of a data packet 106 with two partialpilot sequences 108_1 and 108_2 and a data sequence 110, wherein thedata packet 106 is overlaid (or superimposed) by a short interferer 130.FIG. 8b shows in diagrams receive power and normalized received powerplotted over time for each of the three time slots of FIG. 8a . Thereceive power (sum of signal plus interferer in the used band) is shownas line 132 in all three cases in the diagrams of FIG. 8b . Thenormalized receive power is shown as line 134 in all three cases in thediagrams of FIG. 8 b.

As shown in FIGS. 8a and 8b , the interferer 130 is only for a partialtime of the sub packet duration active, therefore not all symbols havethe same receive power.

The normalization factor is calculated over all symbols in this timeslot. Afterwards this factor is applied to all symbols inside the subpacket length. Therefore the interfered symbols have a much higheramplitude after the normalization.

In the first time slot the interferer is only for a small subset ofsymbols active and the impact of the interferer power in thenormalization factor is very low. In the both other cases the impact ofthe interferer is higher. The normalization decreases all symbols inthis time slot, to get the mean power distribution to one inside thistime slot. The not interfered symbols are also decreased as theinterfered symbols. Afterwards in the correlation the correct symbolsare threaded lower than the interfered symbols. The output after thenormalization is shown with lines 134 in the FIG. 8b . If the interferedsymbols have more impact on the correlation result, false detections arepossible.

If the interferer lengths are unknown or the length is not much greaterthe duration on a sub packet, symbol wise normalization can be done tosolve the problem described before.

The symbol wise normalization works in the same way as the sub packetwise normalization, except of the normalization factors. These arecalculated for each symbol inside the sub packet length separately andnot only one for the whole sub packet length. FIGS. 9a and 9b shows thetechnique.

FIG. 9a shows a schematic view of a data packet 106 with two partialpilot sequences 108_1 and 108_2 and a data sequence 110, wherein thedata packet 106 is overlaid (or superimposed) by a short interferer 130.FIG. 9b shows in diagrams receive power and normalized received powerplotted over time for each of the three time slots of FIG. 9a . Thereceive power (sum of signal plus interferer in the used band) is shownas line 132 in all three cases in the diagrams of FIG. 9b . Thenormalized receive power is shown as line 134 in all three cases in thediagrams of FIG. 9 b.

Each symbol is normalized to the same power, e. g. by division with itsown symbol power. Furthermore the output of the correlation depends onlyon the received phases of the synchronization sequence.

In the correlation all symbols are treated equal and the effect ofinterfered symbols is less than without normalization.

Instead of doing the normalization before the correlation, normalizationof the correlation product is also possible.

The correlation product can be derived using cp1=rp1*conj(p1) in eachtime slot. rp1 is the received synchronization (or pilot) sequence, p1the known ideal synchronization (or pilot) sequence and cp1 is thecorrelation result. This technique can be done with one correlation overthe whole sequence or can be done with sub correlations, as describedbefore.

However, the output signal cp1 may not provide any clear informationwhether a signal was present or not, as also a strong noise impulse canlead to high levels of cp1. Therefore one possibility is thenormalization of the output signal by norm1=abs(rp1)*abs(p1).

The normalized output is then given by cp1norm=cp1/norm1. If the pilotsequence 108 has constant power (which is assumed in the following), thevalue of cp1norm can take values from 0 to 1. The value of 1 indicatesfull correlation. In case signals that do not include the signal p1, theabsolute value of cp1 will be smaller than norm1.

Alternatively, norm1 can be calculated as norm1=abs(rp1)*c, where c is aconstant that can be adjusted that cp1norm reaches a maximum value ofone.

Alternatively, norm1 can be calculated as norm1=sqrt(abs(rp1{circumflexover ( )}2))*c, or norm1=sqrt((abs(rp1)*abs(p1)){circumflex over ( )}2).

Normalization of the input symbols can be done. Normalization is anonlinear technique, e. g. the absolute value or the power is used.There are different techniques which depend on the interferencescenario:

-   -   sub packet wise normalization;    -   telegram wise normalization; and    -   symbol wise normalization

This has the advantage of reducing the impact of interferer in thecorrelation result. Therefore, the number of false detection isdecreased. If a false detection occurs, the decoder tries to decode thepacket, but the CRC (CRC=cyclic redundancy check) fails. If the numberof false detections is decreased, the used CPU time is reduced and otherapplications can use the CPU time or the power consumption of the deviceis lower.

Variance

As described above the packet detection calculates the correlation forall synchronization sequences and the addition of the absolute value ofall sub correlations yields the output. If only one sequence is used,the sequence can be split into sub parts as described before. If thecorrelation value is over a defined threshold, a new packet is detected.This technique works fine, if there are no interferers in the channel.

Another technique is based on the variance of the sub packetcorrelations. The variance for a discrete finite length can becalculated by var=1/n*sum((xi−μ)²). The mean value can be calculated byμ=1/n*sum(xi). In this case, n is the number of used sub correlations, pthe before calculated mean value and xi the correlation result of subcorrelation i.

The partly correlation results are normalized to the receive power andto the length of the correlation part. Therefore the correlation resultof one sub correlation is between 0 and 1.

If no noise and no interferer to the signal are applied, the correlationof each sub correlation at the perfect time slot yields the same valueand no variance between the correlation results of the sub correlationscan be observed. The optimal timeslot is in the middle of theautocorrelation function, where the peak has the highest value. In othertime slots there is high variance caused by unknown data.

The calculation of the variance is shown as an example for sub packetwise correlation in the following figure.

If there is noise on the channel the variance at the perfect time slotincreases with decreasing SNR. The maximum variance can be achieved atthe lowest possible SNR, where packets can correct decoded. This valuecan be used as a threshold. If the calculated variance is below thisthreshold, a packet is detected.

This threshold can be used standalone for the packet detection or can beused in combination with normal detection as a second stage for decisionwhether the detection of the first stage was wrong.

FIG. 10 shows in a diagram a plurality of data packets (or sub-packets,or hops) 106 which are part of a telegram which is transmitted separatedinto the plurality of data packets 106 over a communication channel anda schematic view of a calculation of a variance over all (or at least apart of) data packets (sub-packets) 106. In FIG. 10, the ordinatedescribes the frequency and the abscissa the time.

This algorithm can also used to detect side lobes in the correlation,which are not necessarily from interference. For example, they can occurby a non-ideal correlation sequence.

As an example for a two stage detection, first the correlation can becalculated with the normalized symbols. If the first stage detects apacket, the correlation results of all sub correlations in the detectedtime slot can be used to calculate the variance. If this variance issmaller than the threshold, packet detection can be triggered.

Typically, the threshold of the first stage can be chosen lower thanpeaks of the side lobes. If a value above the threshold is detected, thevariance can be calculated. Only if both values are in the detectionrange, a new packet can be detected.

The correlation for the whole packet can be split into sub correlations.These sub correlations can be also used if only one correlation sequenceis in the whole packet. In this case, the preamble can be split for subcorrelations. Over all sub correlations the variance can be calculatedand compared to a threshold.

Advantage of this technique is, that in the interfered case the numberof false detected packets can reduced. Furthermore the thresholds canreduced, which yields in a better detection rate for low SNRs(SNR=signal-to-noise ratio).

Weighted Synchronization Symbols

Furthermore, the preamble symbols (or pilot symbols) can be weightedbefore the correlation. There are three different techniques:

-   -   weight factors for all sync symbols;    -   weight factors for each sub-packet 106; and    -   weight factors for each preamble part,

The weighing can also be done after the correlation over a sub-packet orover a part of a correlation sequence. Therefore the partial correlationis done and afterwards multiplied with the weight factor.

As an example the weight factors can be calculated by the variance onthe assumed synchronization symbols in the time slot. Or they can beobtained from the power variance of all symbols inside the time slot orbased on a determined signal-to-noise ratio.

Before the correlation is done, the weight factors can be applied to thesynchronization symbols. Interfered synchronization symbols have lowerweight factors, so these symbols have less influence on the correlationresult.

FIG. 11 shows a schematic view of three data packets 106, each of thedata packets 106 having two partial pilot sequences 108_1 and 108_2, andof a weighting of the pilot sequences 108_1 and 108_2 performed byapplying individual weighting factor to each of the partial pilotsequences 108_1 and 108_2 for each data packet 106.

In other words, FIG. 11 shows this concept for preamble part wiseweighting. The factors are multiplied after the summation over thepreamble part and the nonlinear operation. If the weighing is donebefore the correlation, the values in the figure are multiplied with thefactors before the calculation of the absolute value is done.

If one only one correlation sequence is used, this sequence can be splitinto sub sequences. Therefore, every sub-sequence gets an own weightfactor.

The synchronization symbols can be multiplied with a weight factor. It'salso possible that only preamble parts are weighted instead of symbolwise weighting. The weight factor can be applied before the correlationor after a sub-correlation.

This has the advantage that the number of false detection can bedecreased in an interfered channel. Therefore, the power consumption ofthe receiver can be reduced.

Side Lobe Detection

Caused by the non-ideal correlation sequence, side lobes occur in thecorrelation output. These side lobes are deterministic and at a specificoffset from the main lobe. The receiver can calculate these positions,if the correlation sequence is known (which is very often known in thereceiver).

This is shown in the following figure, where the main lobe and two sidelobes are shown. These side lobes have a lower peak than the main lobe.To avoid false detections, the threshold is set to be higher than thebiggest side lobe peak.

If the threshold is set lower than highest side lobe peak, falsedetections occur. To avoid this false detection, the receiver search inthe known side lobe temporal distance, if a higher peak occurs. If yes,a side lobe is detected and if not the receiver has already found themain lobe.

These side lobes can also occur on different frequency offsets. Thereceiver gets the side lobes by doing an autocorrelation function ondifferent frequency offsets.

FIG. 12 shows in a diagram an amplitude of an correlation output plottedover time. In other words, FIG. 12 shows a typical correlation output.On the abscissa the time is plotted and on the ordinate the correlationoutput is shown. The main lobe 136, two side lobes 138 and noise floor140 are shown in FIG. 12.

The additional computation power is very low, because the side lobecorrelation values are calculated earlier in the correlation and can besaved in a history (or memory).

Side lobe detection can be done. If a value above the threshold isfound, the correlation values in side lobe distance are compared to theactual correlation value. If the value in side lobe distance is higher,a side lobe 138 is detected. Otherwise the main lobe 136 is in theactual time slot.

This has the advantage that the threshold for the detection can be setunder the highest peak of a side lobe 138. Thereby, an improveddetection rate can be achieved even for a low signal-to-noise ratio. Thenumber of false detections can be decreased, compared with the samethreshold without side lobe detection.

Detection Window

As previously shown in FIG. 12, there is not an ideal correlation aroundthe main lobe 136. This is caused by non-ideal correlation sequence, bysplitting the correlation parts into the data parts and by interference.Therefore, to avoid false detections, the threshold is set over thehighest value except the main lobe 136, which yields a bad detectionperformance in a noisy channel. At decreasing SNR, the value of thecorrelation results gets lower. Packet detection is only assumed if thecorrelation value above the defined threshold.

To get better performance against noise, a detection window can beintroduced. This window has normally the size of the region before andafter the main lobe 136. Instead of triggering new packet detectiondirectly, if a value above the threshold is detected, the highest peakinside the window is searched. The packet detection output can blockeduntil the index of the highest peak inside the detection window gets apredefined value (detection index). If the correlation value is abovethe threshold and the index is exact at the defined value, packetdetection can be triggered.

FIG. 13 shows such a detection window. In this example it has elevenelements. The detection index can be set of the middle of the window.

FIG. 14 shows a flow-chart of a method 160 for detecting a data packetusing a detection window, according to an embodiment. In a first step162, a time slot (index) can be increased. In a second step 164, thecorrelation can be calculated for the actual time slot. In a third step166, the result (of the correlation) can be inserted in the detectionwindow. In a fourth step 168 a maximum value in the detection window canbe determined. In a fifth step 170 it can be determined if the maximumvalue is greater than a threshold. If the maximum value is not greaterthan the threshold, then first to fifth steps 162 to 170 are repeated.If the maximum value is greater than the threshold, then in a sixth step172 an index of the maximum value is determined. In a seventh step 174it is determined whether the index is equal to the detection index. Ifthe index is not equal to the detection index, then first to seventhsteps 162 to 174 are repeated. If the index is equal to the detectionindex, then in an eight step 176 a new packet is detected.

In other words, FIG. 14 shows a schematic how the detection is done.Before the detection is started the window is created and set withinitial values (e. g. all values to zero). Afterwards the continuousdetection is started.

In the first step 162 the index of the time slot is updated. Afterwards164 the correlation in the actual time slot is done. For thiscorrelation the above mentioned techniques can be used or all othertechniques also work fine. The correlation result is saved in thedetection window at the newest time index 166. Therefore, the oldest oneis deleted from the array (shift all values by one to the right andinsert on the left the new value).

Inside this window the maximum peak is searched 168. If the max peakinside the window is lower than the threshold 170, the process is goingback to the first step 162. Otherwise the index of the maximum isextracted 172 and compared to the detection index 174. If both valuesare the same a new packet is detected 176.

FIG. 15 shows in three diagrams amplitudes of correlation outputs 170plotted over time for three different time slots as well as thethreshold 171 and the detection window 172 used for detecting the datapacket, according to an embodiment.

In other words, FIG. 15 shows this method at three different time slots.In the first part a value above the threshold can be detected, which isnot at the detection index. If packet detection is done in this slot,false detection occurs.

In the detection window 172 the highest value is obtained. Now it'sproved if the highest value inside this window 172 is above thethreshold.

This is the case for the first time slot in FIG. 15. But the index ofthe highest value needs to be exact the detection index, which is notthe case for the first case. The index is greater than the detectionindex, so this peak is in a few steps at the detection index. If it isthere, it has to be the highest value inside the window to trigger thepacket detection. Until it gets closer to the detection index, othercorrelation values added to the window. In this example the have highercorrelation values, so the index of the maximum value is not equal tothe detection index.

In the second case, the highest value is exact at the detection indexand the value is above the threshold, packet detection is assumed.

In the last case the maximum value index is below the middle of thewindow.

If the index of the maximum is higher than the detection index, the timeslot is too early for detection, it will be detected later. If the valueis lower than the detection index, the packet detection was alreadytriggered before.

A detection window 172 can be introduced. If a value above the threshold171 is detected, the packet detection is not triggered immediately.Instead, the packet detection can be blocked, until the index of themaximum value inside the detection window 171 reaches the defineddetection index.

This has the advantage that the threshold can be set lower, which yieldsa better detection rate at low SNRs with less false detection rate.

Partly Correlation

Instead of calculating the correlation over all sub-correlations, thecorrelation can be only done over a part of all correlation sequences.This technique also works, if only one correlation sequence is used. Inthis case, the correlation sequence can be split into sub parts asdescribed before.

FIG. 16 shows in a diagram a plurality of data packets (or sub-packets,or hops) 106 which are part of a telegram which is transmitted separatedinto the plurality of data packets 106 over a communication channel anda schematic view of a partly correlation over three of the data packets(sub-packets) 106. In FIG. 16, the ordinate describes the frequency andthe abscissa the time.

In other words, FIG. 16 gives an example for this technique with subpacket wise correlations. Instead of calculating the correlation overall sub packets, the correlation is done over only three sub packets.Afterwards the sum of the subset yields the correlation output.

The threshold can be adapted to the lower number of sub correlations.

Unfortunately, the minimized correlation sequence has a higherprobability for false detection caused by interferer or by noise. Inorder to get an improved (or even best) performance, a two stagedecision can be used. In a first step, the correlation can be done overa subset of correlation sequences. If a packet is detected in the firststep, in a second step the correlation can be done over all correlationparts. Only if the second correlation is also above the threshold,packet detection may be triggered.

The correlation output of the first stage can be used for thecalculation of the whole correlation. Therefore, the correlation overthe remaining correlations sequences is calculated and added to theresult of the first stage.

The correlation can be only calculated over a subset of thesynchronization sequence. If a packet is detected by this method, asecond correlation over all sequences can be done.

This has the advantage that the consumption power of the receiver can bereduced, because the algorithm must not calculate the correlation of allparts. Only if the sub correlation detects a packet, the wholecorrelation is calculated.

Method

FIG. 17 shows a flowchart of a method 200 for receiving a data packet.The method comprises a step 202 of receiving a data packet comprising apilot sequence; a step 204 of separately correlating the pilot sequencewith at least two partial reference sequences corresponding to areference sequence for the pilot sequence of the data packet, in orderto obtain partial correlation results for the at least two partialreference sequences; and a step 206 of non-coherently adding the partialcorrelation results in order to obtain a correlation result for the datapacket.

Although some aspects have been described in the context of anapparatus, it is clear that these aspects also represent a descriptionof the corresponding method, where a block or device corresponds to amethod step or a feature of a method step. Analogously, aspectsdescribed in the context of a method step also represent a descriptionof a corresponding block or item or feature of a correspondingapparatus. Some or all of the method steps may be executed by (or using)a hardware apparatus, like for example, a microprocessor, a programmablecomputer or an electronic circuit. In some embodiments, one or more ofthe most important method steps may be executed by such an apparatus.

Further Embodiments

FIG. 18 shows a schematic block diagram of a receiver 100 according toan embodiment. The receiver 100 comprises a receiving unit 102 and asynchronization unit 104. The receiving unit 102 is configured toreceive data packets 106 (e.g., at least two data packets), at least twoof the data packets 106 (e.g., each of the at least two data packets)comprising a partial pilot sequence of at least two partial pilotsequences (note that the receiver may receiver additional data packetsnot having a partial pilot sequence).

For example, the receiving unit 102 can be configured to receive anddemodulate a signal transmitted from a transmitter over a communicationchannel to the receiver 100, and to provide based thereon a data streamcomprising the at least two data packets 106.

A first data packet 106 of the at least two data packets 106 cancomprise a first partial pilot sequence 108_1 of the at least twopartial pilot sequences 108_1-108_n and a second data packet 106 cancomprise a second partial pilot sequence 108_2 of the at least twopartial pilot sequences 108_1-108. Further, the at least two datapackets 106 can comprise one or more data sequences 110 arranged beforeor after the partial pilot sequences 108_1 and 108_2.

The synchronization unit 104 is configured to separately correlate thepartial pilot sequences 108_1-108_n with at least two partial referencesequences 112_1-112_n, in order to obtain a partial correlation result116_1-116_n for each of the at least two partial reference sequences112_1-112_n, wherein the synchronization unit 104 is configured tonon-coherently add the partial correlation results 112_1-112_n in orderto obtain a coarse correlation result 118 for the two data packets 106.

For example, the synchronization unit 104 can be configured to correlatethe partial pilot sequence 108_1 of the first data packet 106 with thefirst partial reference sequence 112_1, in order to obtain a partialcorrelation result 116_1 for the first partial reference sequence 112_1,and to correlate the partial pilot sequence 108_2 of the second datapacket 106 with the second partial reference sequence 112_2, in order toobtain a partial correlation result 116_2 for the second partialreference sequence 112_2.

The synchronization unit 104 can be configured to non-coherently add thepartial correlation results 116_1-116_n by adding absolute values orsquared absolute values or approximated absolute values or any othernon-liner operation of the partial correlation results 116_1-116_n.

The at least two partial reference sequences 112_1-112_n can be at leasttwo different parts of a reference sequence 114, wherein the at leasttwo partial pilot sequences 108_1-108_n can be at least two differentparts of a pilot sequence 108.

Thus, compared with the embodiments of the receiver 100 described withrespect to FIGS. 1 to 16, instead of a data packet 106 comprising atleast two partial pilot sequences 108_1-108_n, data packets 106 (e.g.,at least two data packets), at least two of the data packets 106 (e.g.,each of the at least two data packets) comprising a partial pilotsequence of at least two partial pilot sequences are received. However,the functionality of the synchronization unit 104 is practically thesame, i.e., the partial correlation results 112_1-112_n can benon-coherently added in order to obtain the coarse correlation result118. If at least two further data packets are received, in the samemanner, the partial correlation results of the at least two further datapackets can be non-coherently added in order to obtain the coarsecorrelation result for the at least two further data packets. Further,the coarse correlation results for the at least two data packets and theat least two further data packets can be combined to obtain a combinedcoarse correlation result.

It becomes obvious, that the description of the receiver shown andexplained with respect to FIGS. 1 to 16 can also be applied to thereceiver shown in FIG. 18, and vice versa.

FIG. 19 shows a flow-chart of a method 210 for receiving. The method 210comprises a step 212 of receiving data packets (e.g., at least two datapackets), at least two of the data packets (e.g., each of the at leasttwo data packets) comprising a partial pilot sequence of at least twopartial pilot sequences; a step 214 of separately correlating thepartial pilot sequences with at least two partial reference sequences,in order to obtain a partial correlation result for each of the at leasttwo partial reference sequences; and a step 216 of non-coherently addingthe partial correlation results in order to obtain a coarse correlationresult for the two data packets.

General

Embodiments can be used for systems for transmitting small amounts ofdata, for example, sensor data, from a large number of nodes, such asheating, electricity or water meters, to a base station are known. Abase station receives (and possibly controls) a large number of nodes.At the base station more computing power and a more complex hardware,i.e. a receiver with higher performance, is available. In the nodes onlycheap crystals are available, which generally have a frequency offset of10 ppm or more. However, embodiments may also be applied to otherapplication scenarios.

Embodiments provide a plurality of optimized preamble (or pilotsequence) splitting's, that improve interferer robustness.

Embodiments provide a correlation method, which is robust againstfrequency offsets. Thereby, partly correlation is used, which are addedafterwards non-coherently. The non-coherent addition of the partialcorrelations can be used to transmit further information in thepreamble, such as length information.

Embodiments provide several methods using which it is possible toperform packet detection with good performance even if the communicationchannel is disturbed. Some of these methods allow an additional gainwith respect to noise.

Depending on certain implementation requirements, embodiments of theinvention can be implemented in hardware or in software. Theimplementation can be performed using a digital storage medium, forexample a floppy disk, a DVD, a Blu-Ray, a CD, a ROM, a PROM, an EPROM,an EEPROM or a FLASH memory, having electronically readable controlsignals stored thereon, which cooperate (or are capable of cooperating)with a programmable computer system such that the respective method isperformed. Therefore, the digital storage medium may be computerreadable.

Some embodiments according to the invention comprise a data carrierhaving electronically readable control signals, which are capable ofcooperating with a programmable computer system, such that one of themethods described herein is performed.

Generally, embodiments of the present invention can be implemented as acomputer program product with a program code, the program code beingoperative for performing one of the methods when the computer programproduct runs on a computer. The program code may for example be storedon a machine readable carrier.

Other embodiments comprise the computer program for performing one ofthe methods described herein, stored on a machine readable carrier.

In other words, an embodiment of the inventive method is, therefore, acomputer program having a program code for performing one of the methodsdescribed herein, when the computer program runs on a computer.

A further embodiment of the inventive methods is, therefore, a datacarrier (or a digital storage medium, or a computer-readable medium)comprising, recorded thereon, the computer program for performing one ofthe methods described herein. The data carrier, the digital storagemedium or the recorded medium are typically tangible and/ornon-transitionary.

A further embodiment of the inventive method is, therefore, a datastream or a sequence of signals representing the computer program forperforming one of the methods described herein. The data stream or thesequence of signals may for example be configured to be transferred viaa data communication connection, for example via the Internet.

A further embodiment comprises a processing means, for example acomputer, or a programmable logic device, configured to or adapted toperform one of the methods described herein.

A further embodiment comprises a computer having installed thereon thecomputer program for performing one of the methods described herein.

A further embodiment according to the invention comprises an apparatusor a system configured to transfer (for example, electronically oroptically) a computer program for performing one of the methodsdescribed herein to a receiver. The receiver may, for example, be acomputer, a mobile device, a memory device or the like. The apparatus orsystem may, for example, comprise a file server for transferring thecomputer program to the receiver.

In some embodiments, a programmable logic device (for example a fieldprogrammable gate array) may be used to perform some or all of thefunctionalities of the methods described herein. In some embodiments, afield programmable gate array may cooperate with a microprocessor inorder to perform one of the methods described herein. Generally, themethods may be performed by any hardware apparatus.

The apparatus described herein may be implemented using a hardwareapparatus, or using a computer, or using a combination of a hardwareapparatus and a computer.

The apparatus described herein, or any components of the apparatusdescribed herein, may be implemented at least partially in hardwareand/or in software.

The methods described herein may be performed using a hardwareapparatus, or using a computer, or using a combination of a hardwareapparatus and a computer.

The methods described herein, or any components of the apparatusdescribed herein, may be performed at least partially by hardware and/orby software.

While this invention has been described in terms of several embodiments,there are alterations, permutations, and equivalents which will beapparent to others skilled in the art and which fall within the scope ofthis invention. It should also be noted that there are many alternativeways of implementing the methods and compositions of the presentinvention. It is therefore intended that the following appended claimsbe interpreted as including all such alterations, permutations, andequivalents as fall within the true spirit and scope of the presentinvention.

1. A receiver, comprising: a receiving unit configured to receive a datapacket comprising a pilot sequence; and a synchronization unitconfigured to correlate the pilot sequence and a reference sequence, inorder to acquire a correlation result; wherein the synchronization unitis configured to use a correlation window for detecting the data packet,wherein the data packet is detected by detecting the highest peak of allcorrelation peaks exceeding a predefined threshold within thecorrelation window; wherein the correlation window is divided into aplurality of time slots, each time slot having an index associatedtherewith; wherein if a correlation value above the predefined thresholdis detected, the highest peak inside the correlation window is searched,wherein the data packet detection is blocked until the index of thehighest correlation peak inside the detection window reaches a defineddetection index.
 2. The receiver according to claim 1, wherein thesynchronization unit is configured to separately correlate the pilotsequence with at least two partial reference sequences, in order toobtain a partial correlation result for each of the at least two partialreference sequences; wherein the synchronization unit is configured tonon-coherently add the partial correlation results in order to obtain acoarse correlation result for the data packet.
 3. The receiver accordingto claim 2, wherein the synchronization unit is configured tonon-coherently add the partial correlation results by adding absolutevalues or squared absolute values or approximated absolute values or anyother non-linear operation of the partial correlation results.
 4. Thereceiver according to claim 2, wherein the at least two partialreference sequences are at least two different parts of a referencesequence for the pilot sequence of the data packet.
 5. The receiveraccording to claim 2, wherein the data packet comprises at least twopartial reference sequences as the reference sequence.
 6. The receiveraccording to claim 2, wherein the receiving unit is configured toreceive at least two data packets, wherein each of the at least two datapackets comprises a pilot sequence; wherein the synchronization unit isconfigured to separately correlate the pilot sequence of each of the atleast two data packets with at least two partial reference sequencescorresponding to a reference sequence for the pilot sequence of thecorresponding data packet, in order to obtain a partial correlationresult for each of the at least two partial reference sequences for eachof the at least two data packets; wherein the synchronization unit isconfigured to non-coherently add at least a part of the partialcorrelation results for each of the at least two data packets in orderto obtain a coarse correlation result for each of the at least two datapackets; wherein the synchronization unit is configured to combine atleast a part of the coarse correlation results of the at least two datapackets, in order to obtain a combined coarse correlation result.
 7. Thereceiver according to claim 6, wherein the synchronization unit isconfigured to combine the coarse correlation results of the at least twodata packets by using a sum or approximations of an ideal Neyman-Pearsondetector of the coarse correlation results of the at least two datapackets.
 8. The receiver according to claim 6, wherein the at least twodata packets are parts of a telegram which is transmitted separated intothe at least two data packets, wherein the receiver comprises a datapacket combining unit configured to combine the at least two datapackets in order to obtain the telegram.
 9. The receiver according toclaim 2, wherein the synchronization unit is further configured tocoherently add the partial correlation results in order to obtain a finecorrelation result for the data packet.
 10. The receiver according toclaim 6, wherein, if the combined coarse correlation exceeds apredefined threshold, the synchronization unit is further configured tocoherently add the partial correlation results for each of the at leasttwo data packets in order to obtain a fine correlation result for eachof the at least two data packets; wherein the synchronization unit isconfigured to combine the fine correlation results of the at least twodata packets, in order to obtain a combined fine correlation result. 11.The receiver according to claim 2, wherein the synchronization unit isconfigured to estimate a frequency offset of the data packet.
 12. Thereceiver according to claim 11, wherein the data packet comprises aheader information coded in a phase shift of the pilot sequence; whereinthe receiver comprises a header extraction unit configured to extractthe header information from the data packet by applying a frequencycorrection to the data packet using the estimated frequency offset andestimating the phase shift of the pilot sequence.
 13. The receiveraccording to claim 2, wherein the synchronization unit is configured tonormalize the coarse correlation results of the at least two partialreference sequences and to combine the normalized coarse correlationresults of the at least two partial reference sequences, in order toobtain a combined coarse correlation result.
 14. The receiver accordingto claim 2, wherein the synchronization unit is configured to normalizesymbols of the pilot sequence to obtain a normalized pilot sequence andto separately correlate the normalized pilot sequences with the at leasttwo partial reference sequences.
 15. The receiver according to claim 2,wherein the synchronization unit is configured to calculate a varianceof the partial correlation results for the data packet and to detect thedata packet if the variance of the partial correlation results for thedata packet is smaller than or equal to a predefined threshold.
 16. Thereceiver according to claim 2, wherein the synchronization unit isconfigured to apply a weight factor to symbols of the data packet, or toapply an individual weight factor to symbols of each of the at least twopartial pilot sequences according to claim 5, or to apply an individualweight factor to each symbol of the at least two partial pilot sequencesaccording to claim
 5. 17. The receiver according to claim 2, wherein thesynchronization unit is configured to detect a main lobe and side lobesof the correlation and to provide the detected main lobe as correlationresult using known distances between the main lobe and the side lobes.18. A Method, comprising: receiving a data packet comprising a pilotsequence; and correlating the pilot sequence and a reference sequence,in order to obtain a correlation result; wherein a correlation window isused for detecting the data packet, wherein the data packet is detectedby detecting the highest peak of all correlation peaks exceeding apredefined threshold within the correlation window; wherein thecorrelation window is divided into a plurality of time slots, each timeslot having an index associated therewith; wherein if a correlationvalue above the predefined threshold is detected, the highest peakinside the correlation window is searched, wherein the data packetdetection is blocked until the index of the highest correlation peakinside the detection window reaches a defined detection index.
 19. Acomputer-readable medium storing program code for execution by aprocessor for receiving a data packet comprising a pilot sequence; andcorrelating the pilot sequence and a reference sequence, in order toobtain a correlation result; wherein a correlation window is used fordetecting the data packet, wherein the data packet is detected bydetecting the highest peak of all correlation peaks exceeding apredefined threshold within the correlation window; wherein thecorrelation window is divided into a plurality of time slots, each timeslot having an index associated therewith; wherein if a correlationvalue above the predefined threshold is detected, the highest peakinside the correlation window is searched, wherein the data packetdetection is blocked until the index of the highest correlation peakinside the detection window reaches a defined detection index.